webusb: Reject the promise if the device is already open.

device/usb/mojo/device_impl_unittest.cc

Index: device/usb/mojo/device_impl_unittest.cc
diff --git a/device/usb/mojo/device_impl_unittest.cc b/device/usb/mojo/device_impl_unittest.cc
index 626edd912491860d08106218b927ce0e0c5eeea2..c6c2e495053e8461831093d9a0242b9811d83f2e 100644
--- a/device/usb/mojo/device_impl_unittest.cc
+++ b/device/usb/mojo/device_impl_unittest.cc
@@ -459,10 +459,19 @@ TEST_F(USBDeviceImplTest, Open) {
 
   EXPECT_CALL(mock_device(), Open(_));
 
-  base::RunLoop loop;
-  device->Open(
-      base::Bind(&ExpectOpenAndThen, OpenDeviceError::OK, loop.QuitClosure()));
-  loop.Run();
+  {
+    base::RunLoop loop;
+    device->Open(base::Bind(&ExpectOpenAndThen, OpenDeviceError::OK,
+                            loop.QuitClosure()));
+    loop.Run();
+  }
+
+  {
+    base::RunLoop loop;
+    device->Open(base::Bind(&ExpectOpenAndThen, OpenDeviceError::ALREADY_OPEN,
+                            loop.QuitClosure()));
+    loop.Run();
+  }
 
   EXPECT_CALL(mock_handle(), Close());
 }